Core materials of a transformer and an electric motor are required to have a high magnetic flux density and low iron loss in order to increase the efficiency of these devices and miniaturize the devices.
As magnetic alloys supplied as such core materials, Fe-Si alloys and the like are known, and widely brought into practical use as non-oriented magnetic steel sheets. Namely, the method of increasing the amount of Si or Al added is known as a method having the effect of increasing resistivity to decrease an eddy current loss, and widely used. However, addition of an alloy component such as Si, Al, or the like decreases the saturation magnetic flux density. The method of increasing the amount of Si or Al added is difficult to satisfy both a low iron loss and high magnetic flux density.
An example of methods of improving an iron loss without adding an alloy component such as Si, Al, or the like is a method comprised of applying several % skin pass rolling to a cold rolled and annealed sheet, stamping by a user, and then applying stress relief annealing. However, this method requires a finish hot rolling temperature of 800.degree. C. or more, 75% or more of cold rolling, and high-temperature annealing for a shot time, as well as several % skin pass rolling. When a coiling temperature after hot rolling is low and recrystallization is insufficient, this method also requires a hot-rolled sheet annealing. Therefore, the method has disadvantages in which the production process is significantly complicated, and the production cost is increased.
Japanese Examined Patent Publication No. 7-23509 discloses a method of improving magnetic properties without complicating the production process. This publication discloses that the Si amount is decreased to 1% or less, and ferrite coarse particles are rolled in a hot rolling step between rough hot rolling and finish hot rolling, improving both an iron loss and a magnetic flux density. However, this method increases less resistivity because the Si content is as low as 1% or less, and thus it cannot sufficiently decrease an iron loss. As a result of investigation, the inventors found that even when this method is applied to steel containing over 1% or Si, the sufficient effect on improving magnetic properties cannot be obtained.
Various attempts have been made to improve a texture. Japanese Unexamined Patent Publication No. 54-110121 discloses that an iron loss is decreased, and particularly, a magnetic flux density is increased when crystal grains in the {011}&lt;100&gt; orientation, i.e., the Goss orientation, are enriched. The Goss orientation generally improves magnetic properties in the L direction, and consequently improves average magnetic properties including those in the C direction. However, the magnetic properties in the C direction are improved only to some extent, and thus improvement in average magnetic properties is limited.
On the other hand, {100}&lt;001&gt; orientation, i.e., regular cubic orientation, is known to simultaneously improve magnetic properties in the two directions including the L direction and the C direction. However, in order to obtain a structure integrated only in the regular cubic orientation, a complicated, long-term and high-cost process is required, such as the high-temperature region intermediate annealing method disclosed in Japanese Examined Patent Publication No. 46-23814, the bidirectional rolling method disclosed in Japanese Unexamined Patent Publication No. 5-271883, the quenched ribbon method disclosed in Japanese Unexamined Patent Publication No. 5-306438, the method of .gamma..fwdarw..alpha. transformation accompanied by decarbonization disclosed in Japanese Unexamined Patent Publication No. 1-108345, etc., thereby failing to establish industrial practicability.
Furthermore, as means for improving magnetic properties, it is useful to accelerate the production of crystal gains in the orientation in which magnetic properties are improved, and suppress the production of crystal grains in the orientation in which magnetic properties are deteriorated. Particularly, crystal grains in the orientation in which magnetic properties are deteriorated include crystal grains in the &lt;111&gt;//ND (the direction perpendicular to a steel sheet plane) orientation. It is preferable to suppress the crystal grains in this orientation, but the above-described special means and high-cost process are required. Therefore, the conventional process for producing a non-oriented magnetic steel sheet is difficult to decrease the grains in the &lt;111&gt;//ND orientation.
Namely, magnetic steel sheets produced in these methods cannot satisfy a low iron loss which is required from the viewpoint of global environment and energy environment at present.